Resilient cation exchange membranes

ABSTRACT

A resilient cation exchange membrane including a porous matrix impregnated with a cross-linked homogenous ion-transferring polymer that fills the pores and substantially covers the surfaces of the porous matrix. The cross-linked homogenous ion-transferring polymer formed by polymerizing a homogeneous solution including (i) a hydrophilic ionic monomer selected from a group consisting of 2-acrylamido-2-methyl-1-propanesulfonic acid, 2-acrylamido-2-methyl-1-propanesulfonic acid salts, sodium 4-vinylbenzenesulfonate, and 3-sulfopropyl acrylate potassium, with (ii) a hydrophobic cross-linking oligomer selected from a group consisting of polyurethane oligomer diacrylate, polyester oligomer diacrylate, epoxy oligomer diacrylate, polybutadiene oligomer diacrylate, silicone diacrylate, dimethacrylate counterparts thereof, polyurethane oligomers having three or more vinyl groups, polyester oligomers having three or more vinyl groups, and mixtures thereof.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.13/877,322, filed 4 Oct. 2011, which application is a US National Stageof International Application No. PCT/CA2011/001115, filed 4 Oct. 2011,which claims the benefit of U.S. Provisional Patent Application No.61/500,466, filed 23 June 2011 and U.S. Provisional Patent ApplicationNo. 61/389,420, filed 4 Oct. 2010, the entire contents and substance ofall are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to ion-exchange membranes. More particularly,this invention relates to resilient cation exchange membranes includinga porous matrix impregnated with a cross-linked homogenousion-transferring polymer that fills the pores and substantially coversthe surfaces of the porous matrix.

2. Description of Related Art

Ion-exchange membranes are used in a wide range of electrodialysis,electrolysis, and diffusion dialysis systems where selective transportof ions takes place under the influence of ion concentration gradientsor electrical potential gradients as the driving force. The initialindustrial applications of ion exchange membranes were focused ondesalinization of saline water to produce potable water supplies.However, ion-exchange membranes are now widely used in many industrialand municipal applications exemplified by purification of drinkingwater, wastewater treatment, demineralization of amino acids, processingof whey waste streams, production of sugar liquors, de-salting dieselfuels, recovery of useful components from fluid process waste streamse.g., metal ions from electroplating systems, purification of organicsubstances, and the like.

Ion exchange membranes generally comprise a polymeric material to whichare attached negatively charged ion groups, or alternatively, positivelycharged ion groups. The counterion of each group is the transferableion. Anion exchange membranes are provided with positively chargedgroups bound to the polymeric material and have mobile negativelycharged anions. Cation exchange membranes are provided with negativelycharged groups fixed to the polymeric material and have mobilepositively charged cations. Ion exchange membrane properties aregenerally determined by the amount, the type and the distribution of thefixed ionic groups. There are four categories of ion exchange membranesbased on their ionic properties, i.e., strong acid membranes, strongbase membranes, weak acid membranes, and weak base membranes. Strongacid membranes typically have sulfonic as the negative charged group,while weak acid membranes have carboxyl acid as the negative chargedgroup. Strong base membranes generally have quaternary amines as thepositive charged group, while weak base membranes have tertiary aminesas the positive charged group. Ideally, a well-performing ion exchangemembrane should have high ion selectivity, low electrical resistance,good mechanical properties, and high stability.

Electrodialysis systems transport ions from a first solution to a secondsolution under the influence of an applied electric potential differencethrough a cation ion exchange membrane and an anion exchange membranesituated and fixed as the opposing walls of an electrodialysis cell. Thecell consists of a “feed” compartment (also commonly referred to as a“diluate” compartment) and a “concentrate” compartment (also commonlyreferred to as a “brine” compartment) formed by an anion exchangemembrane and a cation exchange membrane, each attached to an electrode.The anion exchange membrane and the cation exchange membrane are bothimpermeable to water molecules. Adjacent cells form a cell pair having:(i) a feed or diluting compartment, and (ii) a brine or concentratingcompartment. For example, a water desalination electrodialysis cell pairwould have a common cation exchange membrane separating the feedcompartment and brine compartment. A first anion exchange membrane onone side of the cation exchange membrane provides and defines the outersurface of the feed i.e., the diluting cell. The first anion exchangemembrane is attached to a first electrical terminal and will be an anodewhen an electrical charge is applied. A second anion membrane providesand defines the outer surface of the brine i.e., the concentrating cell.The second anion exchange membrane is attached to a second electricalterminal and will be cathode when an electrical charge is applied. Inthe diluting cell, cations will pass through the cation transfermembrane facing the anode (i.e., the first anion exchange membrane), butwill be stopped by the paired anion transfer membrane of theconcentrating cell in that direction facing the cathode (i.e., thesecond anion exchange membrane). Similarly, anions pass through theanion transfer membrane of the diluting cell facing the cathode, butwill be stopped by the cation transfer of membrane of the adjacent pairfacing the anode. In this manner, salt in a diluting cell will beremoved and in the adjacent concentrating cell, cations will be enteringfrom one direction and anions from the opposite direction.

The large throughput volumes required for commercial desalinationprocesses generally require configuration of multiple electrodialysiscell pairs into an electrodialysis stack, with alternating anion andcation exchange membranes forming the multiple electrodialysis cells.Each membrane stack has a DC (direct current) anode at one end of thestack and a DC cathode at the other end. Under a DC voltage, ions moveto the electrode of opposite charge. Flow in the electrodialysis stackis arranged so that the dilute and concentrated flows are kept separateand a desalinated water stream is produced from the dilute flow. Becausethe quantities of dissolved ions in feed streams are far less than ionconcentrations in the brines, electrodialysis stacks facilitate highvolume throughputs of fluids for desalination

Ionic salts commonly build up at the membrane surfaces inelectrodialysis systems in the direction of electric flow therebyreducing the rates of ion flow through the membranes resulting inreduced desalination efficiencies and reduced throughput volumes. Theaccumulation of ions on the membrane surfaces can be overcome byperiodically reversing the direction of ion flows by reversing thepolarity of the electrodes on a regular basis thereby changing the“anode” membranes into “cathode” membranes and vice versa. Theconsequence is that the dilute and concentrate flows are simultaneouslyswitched with the concentrate becoming the dilute flow and vice versa,enabling removal and flushing of ionic fouling deposits. This process isgenerally referred to as electrodialysis reversal (EDR) and is commonlyused in most commercial electrodialysis systems.

Ion exchange membranes used in electrodialysis stacks for separationand/or recovery of ions from saline water, industrial processing liquidfeedstocks and brines, are firmly fixed in place to prevent leakage ofwater between the cells and undergo considerable mechanical stress andstrain due to considerable physical and hydrostatic pressures exertedduring throughput and desalination of high volumes of fluids. Mechanicalstresses and strains are exacerbated in systems that incorporateelectrodialysis reversal. Repeated stress-strain pressure changes resultin the occurrence of stress lines that result in membrane fractures andfailures. Occurrence of stress lines in ion exchange membranes can alsobe caused by changes in osmotic pressure fluctuations as theconcentrated brines receiving ions separated from fluids flowing throughthe diluant cells, and subsequently can result in membrane failures.

Most commercial ion exchange membranes are composite materials generallyprepared by the copolymerization of a cross-linking divinyl monomer anda monomer containing ion exchange groups onto a selected membranesupport material to overcome the problems of brittleness and poormechanical stability associated with ion exchange resins. Membranesupports commonly used for manufacture of ion-exchange membranes includesolid non-porous sheets of polyvinyl chloride (PVC) or low-densitypolyethylene (LDPE), and porous fabrics woven from PVC and/or LDPEstrands. The cross-linked divinyl monomers and monomers having ionexchange groups can be applied to the membrane supports as poured-on orpasted-on coatings to impregnate the membrane supports. Alternatively,the ion-exchange membranes can be prepared by lamination of the membranesupports with divinyl monomers and ion exchange monomers followed bycuring. However, the problem of ion-exchange membrane failure due tostress-strain pressures and/or osmotic fluctuations remains asignificant industry concern.

Most commercially available ion exchange membranes are manufactured bymulti-step processes using copolymers of styrene and divinylbenzene thatare subsequently modified by addition of ion exchange moieties. Theproblem with ion exchange membranes comprising styrene divinylbenzenecopolymers, particularly when they are further polymerized withcompounds having short cross-linking chains, is that they tend to bebrittle and non-resilient and consequently fracture under pressure andstrain loads. Furthermore, the multi-step processes generally involveuse of hazardous chemicals exemplified by styrene, divinylbenzene,concentrated sulfuric acid, and halogenated chemicals among others, andrequire elaborate safety precautions incorporated into the manufacturingfacilities and waste stream handling systems to mitigate issuesassociated with worker health issues, and environmental toxicity. Inaddition to the need for more durable and more flexible ion-exchangemembranes, there is also a concomitant need for producing such membranesusing methods that are less toxic and more cost-effective.

BRIEF SUMMARY OF THE INVENTION

The embodiments of the present invention pertain to processes forproducing resilient ion exchange membranes. Some embodiments pertain toresilient ion exchange membranes produced by the processes that havedurability to withstand stress-strain pressures during operational use.

In an exemplary embodiment, a resilient cation exchange membranecomprises a porous matrix selected from a group consisting ofpolyesters, polyvinyl chlorides, low-density polyethylenes,very-low-density polyethylenes, polypropylenes, polysulfones, nylons,nylon-polyamides, and mixtures thereof, the porous matrix impregnatedwith a cross-linked homogenous ion-transferring polymer that fills thepores and substantially covers the surfaces of the porous matrix, thepolymer formed by polymerizing a homogeneous solution comprising (i) ahydrophilic ionic monomer selected from a group consisting of2-acrylamido-2-methyl-1-propanesulfonic acid,2-acrylamido-2-methyl-1-propanesulfonic acid salts, sodium4-vinylbenzenesulfonate, and 3-sulfopropyl acrylate potassium, with (ii)a hydrophobic cross-linking oligomer selected from a group consisting ofpolyurethane oligomer diacrylate, polyester oligomer diacrylate, epoxyoligomer diacrylate, polybutadiene oligomer diacrylate, siliconediacrylate, dimethacrylate counterparts thereof, polyurethane oligomershaving three or more vinyl groups, polyester oligomers having three ormore vinyl groups, and mixtures thereof.

Another exemplary embodiment of the present invention pertains to aprocess for producing a resilient ion exchange membrane, that generallycomprises the steps of (1) selecting a porous matrix, (2) saturating theporous matrix with a homogenous solution comprising mixture of: (i) ahydrophilic ionic monomer, (ii) a hydrophobic cross-linking oligomerand/or a comonomer, (iii) a free radical initiator, and (iii) a solventselected for solubilizing the hydrophilic ionic monomer, the hydrophobiccross-linking oligomer and/or comonomer, and the free radical initiatorinto a homogenous mixture, (3) removing excess homogenous solution fromthe saturated porous matrix, (4) polymerizing the hydrophilic andhydrophobic components in the homogenous solution to form a cross-linkedion-transferring polymer that substantially fills the pores andsubstantially covers the surfaces of the porous matrix thereby producingthe resilient ion exchange membrane of the present invention, (5)washing the resilient ion exchange membrane to remove excess solvent,and (6) optionally bathing the washed resilient ion exchange membrane ina sodium chloride solution to convert the ion exchange membrane into asodium form or into a chloride form.

According to one aspect, the process produces resilient cation exchangemembranes by incorporating into the homogenous solution hydrophilicionic monomers selected from a group consisting of2-acrylamido-2-methyl-1-propanesulfonic acid, sodium4-vinylbenzenesulfonate, 3-sulfopropyl acrylate potassium, and theirsalts.

According to another aspect, the process produces resilient anionexchange membranes by incorporating into the homogenous solutionhydrophilic ionic monomers selected from a group consisting of3-methacryloylaminopropyl trimethylammonium chloride, vinylbenzyltrimethylammonium, 3-acrylamidopropyl trimethylammonium chloride,2-acryloyloxyethyl trimethylammonium chloride, 3-methacryloylaminopropyltrimethylammonium chloride, and mixtures thereof.

According to another aspect, the process produces resilient ion exchangemembranes by incorporating into the homogenous solution one or morehydrophobic cross-linking oligomers and/or comonomers selected from agroup consisting of polyurethane oligomer diacrylate, polyester oligomerdiacrylate, polyether oligomer diacrylate, epoxy oligomer diacrylate,polybutadiene oligomer diacrylate, silicone diacrylate, hexanedioldiacrylate, decanediol diacrylate, and their dimethacrylate counterpartsthereof, and mixtures thereof. Alternatively, the hydrophobiccross-linking oligomers and/or comonomers may be selected from a groupconsisting of polyurethane oligomers having three or more reactive vinylgroups, polyester oligomers having three or more reactive vinyl groups,polyether oligomers having three or more reactive vinyl groups,counterparts thereof, and mixtures thereof.

Another embodiment of the present invention pertains to a resilientcation exchange membrane comprising: (1) a porous matrix selected from agroup consisting of polyesters, polyvinyl chlorides, low-densitypolyethylenes, very-low-density polyethylenes, polypropylenes,polysulfones, nylons, nylon-polyamides, and mixtures thereof; to whichare cross-linked (2) a hydrophilic ionic monomer selected from a groupconsisting of 2-acrylamido-2-methyl-1-propanesulfonic acid, sodium4-vinylbenzenesulfonate, 3-sulfopropyl acrylate potassium, and saltsthereof; and (3) a hydrophobic cross-linking oligomer and/or ahydrophobic cross-linking comonomer selected from a group consisting ofpolyurethane oligomer diacrylate, polyester oligomer diacrylate,polyether oligomer diacrylate, epoxy oligomer diacrylate, polybutadieneoligomer diacrylate, silicone diacrylate, hexanediol diacrylate,decanediol diacrylate, and their dimethacrylate counterparts thereof,and mixtures thereof, and mixtures thereof. Alternatively, thehydrophobic cross-linking oligomers and/or comonomers may be selectedfrom a group consisting of polyurethane oligomers having three or morereactive vinyl groups, polyester oligomers having three or more reactivevinyl groups, polyether oligomers having three or more reactive vinylgroups, counterparts thereof, and mixtures thereof. The resilient cationexchange membranes of the present invention generally have the followingproperties: (i) a membrane thickness in the range of about 0.06 mm toabout 0.15 mm; (ii) an electrical resistance in the range of about 0.8 Ωcm² to about 3.0 Ω cm²; (iii) a water content in the range of about 20%to about 45% by wt.; and (iv) an ion exchange capacity from the range ofabout 1.3 mmol to about 2.5 mmol per g of dry resin.

Another embodiment of the present invention pertains to a resilientanion exchange membrane comprising: (1) a porous matrix selected from agroup consisting of polyesters, polyvinyl chlorides, low-densitypolyethylenes, very-low-density polyethylenes, polypropylenes,polysulfones, nylons, nylon-polyamides, and mixtures thereof; to whichare cross-linked (2) a hydrophilic ionic monomer selected from a groupconsisting of 3-methacryloylaminopropyl trimethylammonium chloride,vinylbenzyl trimethylammonium, 3-acrylamidopropyl trimethylammoniumchloride, 2-acryloyloxyethyl trimethylammonium chloride,3-methacryloylaminopropyl trimethylammonium chloride, and mixturesthereof; and (3) a hydrophobic cross-linking oligomer and/or ahydrophobic cross-linking comonomer selected from a group consisting ofpolyurethane oligomer diacrylate, polyester oligomer diacrylate,polyether oligomer diacrylate, epoxy oligomer diacrylate, polybutadieneoligomer diacrylate, silicone diacrylate, hexanediol diacrylate,decanediol diacrylate, and their dimethacrylate counterparts thereof,and mixtures thereof, and mixtures thereof. Alternatively, thehydrophobic cross-linking oligomers and/or comonomers may be selectedfrom a group consisting of polyurethane oligomers having three or morereactive vinyl groups, polyester oligomers having three or more reactivevinyl groups, polyether oligomers having three or more reactive vinylgroups, counterparts thereof, and mixtures thereof. The resilient anionexchange membranes of the present invention generally have the followingproperties: (i) a membrane thickness in the range of about 0.06 mm toabout 0.15 mm; (ii) an electrical resistance in the range of about 0.8 Ωcm² to about 3.0 Ω cm²; (iii) a water content in the range of about 20%to about 45% by wt.; and (iv) an ion exchange capacity from the range ofabout 1.3 mmol to about 2.5 mmol per g of dry resin.

BRIEF DESCRIPTION OF THE DRAWINGS

Various features and advantages of the present invention may be morereadily understood with reference to the following detailed descriptiontaken in conjunction with the accompanying drawings, wherein likereference numerals designate like structural elements, and in which:

FIG. 1 is a chart showing desalination of a salt solution by passagethrough an electrodialysis microstack assembled with exemplary anionexchange membranes and exemplary cation exchange membranes according toone embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

To facilitate an understanding of the principles and features of thevarious embodiments of the invention, various illustrative embodimentsare explained below. Although exemplary embodiments of the invention areexplained in detail, it is to be understood that other embodiments arecontemplated. Accordingly, it is not intended that the invention islimited in its scope to the details of construction and arrangement ofcomponents set forth in the following description or examples. Theinvention is capable of other embodiments and of being practiced orcarried out in various ways. Also, in describing the exemplaryembodiments, specific terminology will be resorted to for the sake ofclarity.

It must also be noted that, as used in the specification and theappended claims, the singular forms “a,” “an” and “the” include pluralreferences unless the context clearly dictates otherwise. For example,reference to a component is intended also to include composition of aplurality of components. References to a composition containing “a”constituent is intended to include other constituents in addition to theone named.

Also, in describing the exemplary embodiments, terminology will beresorted to for the sake of clarity. It is intended that each termcontemplates its broadest meaning as understood by those skilled in theart and includes all technical equivalents which operate in a similarmanner to accomplish a similar purpose.

Ranges may be expressed herein as from “about” or “approximately” or“substantially” one particular value and/or to “about” or“approximately” or “substantially” another particular value. When such arange is expressed, other exemplary embodiments include from the oneparticular value and/or to the other particular value.

Similarly, as used herein, “substantially free” of something, or“substantially pure”, and like characterizations, can include both being“at least substantially free” of something, or “at least substantiallypure”, and being “completely free” of something, or “completely pure”.

By “comprising” or “containing” or “including” is meant that at leastthe named compound, element, particle, or method step is present in thecomposition or article or method, but does not exclude the presence ofother compounds, materials, particles, method steps, even if the othersuch compounds, material, particles, method steps have the same functionas what is named.

It is also to be understood that the mention of one or more method stepsdoes not preclude the presence of additional method steps or interveningmethod steps between those steps expressly identified. Similarly, it isalso to be understood that the mention of one or more components in acomposition does not preclude the presence of additional components thanthose expressly identified.

The materials described as making up the various elements of theinvention are intended to be illustrative and not restrictive. Manysuitable materials that would perform the same or a similar function asthe materials described herein are intended to be embraced within thescope of the invention. Such other materials not described herein caninclude, but are not limited to, for example, materials that aredeveloped after the time of the development of the invention.

The embodiments of the present invention relate to processes forproducing resilient ion exchange membranes that have excellentmechanical stability in that they are flexible and resistant to theformation of stress lines, fractures, and the occurrence of crackingduring use. The embodiments also relate to resilient ion exchangemembranes produced by the processes of the present invention.

An embodiment of the present invention pertains to a process forproducing an exemplary flexible ion exchange membrane having resilientdeformation properties that resist the formation of stress lines and/orfractures across and through the membrane's inner and outer surfaces.The process comprises the steps of preparing a homogenous solutioncomprising a mixture of: (i) one or more hydrophilic ionic monomercomponents, (ii) one or more hydrophobic long-chain cross-linkingoligomer components and/or one or more hydrophobic cross-linkingcomonomer components, (iii) a free radical initiator, and (iv) one ormore solvents that have the capacity to solubilise the hydrophiliccomponents, the hydrophobic components, and the free radical initiator,and then keep components solubilised in a homogenous solution withouttheir separation into hydrophilic and hydrophobic phases. A suitableporous matrix is saturated with the homogenous solution after which,excess solution is removed while taking measures to avoid formation ofair pockets and/or bubbles, resulting in the porous matrix beingimpregnated by the homogenous solution and with both surfaces of theporous matrix being coated by a film of the homogenous solution. Theimpregnated and coated porous structure is cured by activation of thefree radical initiator consequently resulting in formation of ahomogenous polymeric gel within, throughout, and about the porous matrixwithout the occurrence of any macrophase separation of the hydrophilicand hydrophobic components, thereby producing the flexible and resilientmembrane. The resilient ion exchange membrane is then washed to removeexcess solvent, and may be optionally bathed in a sodium chloridesolution.

The resilient ion exchange membranes produced by the process of thepresent invention comprise porous substrates impregnated with andcovered by homogenous polymeric gels within, throughout, and about thesubstrates. The water content of the resilient ion exchange membranescan be adjusted to within selected target ranges by adjusting theconcentrations of the solvents in the homogenous solutions used toprepare the ion exchange membranes.

According to one aspect, the porous matrix may comprise a woven fabric,a non-woven sheet material, or a microporous substrate.

Suitable woven fabrics may be woven from strands selected from one ormore of materials exemplified by polyester, PVC, LDPE, very-low-densitypolyethylene (VLDPE), polypropylene, polysulfone, nylon,nylon-polyamides. Suitable polyesters are exemplified by polyglycolideor polyglycolic acid (PGA), polylactic acid (PLA), polycaprolactone(PCL), polyethylene adipate (PEA), polyhydroxyalkanoate (PHA),polyethylene teraphthalate (PET), polybutylene teraphthalate (PBT),polytrimethylene teraphthalate (PTT), polyethylene naphthalate (PEN),and Vectran®, a fiber spun from a liquid crystal polymer formed by thepolycondensation of 4-hydroxybenzoic acid and6-hydroxynaphthalene-2-carboxylic acid (Vectran is a registeredtrademark of Kuraray Co. Ltd., Kurashiki City, Japan). PET isparticularly suitable for producing a woven fabric matrix for theflexible ion exchange membrane of the present invention.

Suitable non-woven sheet material may comprise sections of a singlesheet comprising a material exemplified by polyester, PVC, LDPE, VLDPE,polypropylene, polysulfone, nylon, nylon-polyamides. Suitable polyestersare exemplified by polyglycolide or PGA, PLA, PCL, PEA, PHA, PET, PBT,PTT, and PEN. Also suitable is a sheet material that comprising two ormore laminations of combinations of sheet material exemplified by PVC,LDPE, VLDPE, polypropylene, polysulfone, nylon, nylon-polyamides.Suitable polyesters are exemplified by polyglycolide or PGA, PLA, PCL,PEA, PHA, PET, PBT, PTT, and PEN.

Suitable microporous sheet material may comprise sections of a singlesheet microporous matrix comprising a material exemplified by polyester,PVC, LDPE, VLDPE, polypropylene, polysulfone, nylon, nylon-polyamides.Suitable polyesters are exemplified by polyglycolide or PGA, PLA, PCL,PEA, PHA, PET, PBT, PTT, and PEN.

Another embodiment of the present invention pertains to homogenoussolutions for preparing the resilient ion exchange membranes of thepresent invention that comprise selected porous matrices as the membranesubstrates. The homogenous solutions comprise mixtures of one or morehydrophilic ionic monomer components, one or more hydrophobiccross-linking oligomer components and/or comonomer components, and oneor more free radical initiators, wherein all of the components aresolubilised in a solvent or mixture of solvents that are capable ofmaintaining the components in a homogenous solutions without anyseparation into hydrophilic and hydrophobic phases.

One aspect pertains to hydrophilic ionic monomers that are suitable forincorporation into the homogenous solution used to impregnate the porousmatrix.

Suitable hydrophilic ionic monomers for preparing cation exchangemembranes are exemplified by 2-acrylamido-2-methyl-1-propanesulfonicacid (AMPS) and its salts, sodium 4-vinylbenzenesulfonate and its salts,and 3-sulfopropyl acrylate potassium and its salts. Sodium4-vinylbenzenesulfonate also known by its tradenames Kayexelate,Resonium A, and Kionex® (Kionex is a registered trademark of Paddocklaboratories Inc., Minneapolis, Minn., USA).

Suitable hydrophilic ionic monomers for preparing anion exchangemembranes are exemplified by 3-methacryloylaminopropyl trimethylammoniumchloride (MAPTAC), vinylbenzyl trimethylammonium, 3-acrylamidopropyltrimethylammonium chloride, 2-acryloyloxyethyl trimethylammoniumchloride, and 3-methacryloylaminopropyl trimethylammonium chloride.

Another aspect pertains to selected hydrophobic cross-linking oligomersand comonomers that are suitable for incorporation into the homogenoussolution used to impregnate and overlay the porous matrix. The functionof the hydrophobic cross-linking oligomers and/or comonomers is toincrease the ductility of the ion exchange resins thereby allowingabsorption of the energy of deformation and resulting in an ion exchangemembrane that resiliently deforms under a stress and/or a strainpressure instead of forming a stress line and/or fracturing. Morespecifically, membranes that are cross-linked with hydrophobic oligomersand/or comonomers have a relatively low Young's modulus that improvesthe membranes' resilience while also increasing their toughness whenexposed to stress pressures and/or strain pressures. Suitablehydrophobic cross-linking oligomers and comonomers preferably have twovinyl bonds as exemplified by polyurethane oligomer diacrylate,polyester oligomer diacrylate, polyether oligomer diacrylate, epoxyoligomer diacrylate, polybutadiene oligomer diacrylate, siliconediacrylate, hexanediol diacrylate, decanediol diacrylate, and theirdimethacrylate counterparts thereof, and mixtures thereof. Also suitableare hydrophobic cross-linking oligomers and comonomers that havemultiple vinyl functionalities as those exemplified by tetrafunctionalepoxy acrylate oligomers (e.g., product number CN2204, Sortomer USA LLC,Exton, Pa., USA), hexafunctional aliphatic urethane acrylates (e.g.,product number CN9006, Sortomer USA LLC), trifunctional aliphaticurethane acrylates (e.g., product number CN989, Sortomer USA LLC),multifunctional urethane acrylate oligomers (e.g., product numberCN9013, Sortomer USA LLC), and the like.

Another aspect pertains to selection of free radical initiators foraddition into the homogenous solutions of the present invention. Thereare three phases that occur during cross-linking polymerizationreactions: (i) stimulation/initiation of the release of free radicalsfrom the free radical initiator compound to catalyze a polymerizationreaction between monomers and oligomers and/or comonomers, (ii)propagation of the polymerization reaction, and (iii) termination of thepolymerization reaction. The rate of reaction during the first step isdependent on the chemical composition of the free radical initiator andthe energy intensity of the stimulus that initiates the rapid release offree radicals that subsequently react with the vinyl groups of thehydrophobic cross-linkers to initiate the polymerization process Therates of reaction of the later steps of propagation and termination ofthe polymerization reaction are a function of vinyl bond concentrationsin the oligomers and/or comonomers, and the rate constants for thepropagation and termination reactions. Common forms of stimuli used toinitiate the release of free radicals from free radical initiators areexemplified by UV photoinitiation, thermal initiation, addition of amaterial to initiate a redox reaction to release free radicals, andradiation with electron beams. Particularly suitable are free radicalinitiators stimulated to release free radicals by irradiation with UVlight (i.e., photo initiators) or by thermal radiation (i.e., thermalinitiators).

Suitable free radical initiators that release free radicals uponexposure to UV light are exemplified by .alpha.-hydroxy ketones freeradical initiators, benzoin ethers, benzil ketals, .alpha.-dialkoxyacetophenones, .alpha.-hydroxy alkylphenones, .alpha.-aminoalkylphenones, acylphosphine oxides, benzophenons/amines,thioxanthone/amines, and titanocenes. Suitable .alpha.-hydroxy ketonefree radical initiators are exemplified by2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone,2-hydroxy-2-methyl-1-phenyl-1-propanone,1-hydroxy-cyclohexyl-phenyl-ketone,-hydroxy-cyclohexyl-phenyl-ketone:benzophenone, and mixtures thereof.Suitable free radical free radical initiators are exemplified2,2′-Azobis(2-methylpropionitrile), benzoyl peroxide,1,7-bis(9-acridinyl)heptane,2-hydroxy-[4′-(2-hydroxypropoxy)phenyl]-2-methyl propanone,4,4′bis(diethylamino)benzophenone,4,4′,4″-methylidynetris(N,N-dimethylaniline),2-hydroxy-2-methyl-1-(4-tert-butyl)phenyl propanone,2-Benzyl-2-(dimethylamino)-4′-morpholinobutyrophenone,1-hydroxycyclohexyl phenylketone,2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one,4-methylbenzophenone, 4-phenylbenzophenone,2-hydroxy-2-methyl-1-phenylpropanone, 2,2′-bis-(2-chlorophenyl),4′,5,5′-tetraphenyl-1,2′biimidazole,2,2-Dimethyoxy-2-phenylacetophenone,4-benzoyl-4′-methyldiphenylsulphide, benzophenone, 2-chlorothioxanthone,2,4-diethylthioxanthone, 2-isopropylthioxanthone, methyl benzoylformate,methyl-o-benzoylbenzoate, 2,4,6-trimethylbenzoyl-diphenyl phosphineoxide, ethyl(2,4,6-Trimethylbenzoyl)-phenyl phosphinate, and mixturesthereof.

Suitable free radical thermal initiators that release free radicals uponexposure to thermal radiation are exemplified by azo-compound thermalinitiators and by peroxide-compound thermal initiators. Suitableazo-compound thermal initiators are exemplified by1,1′-azobis(cyclohexanecarbonitrile), 2,2′-azobis(isobutyronitrile),2,2′-azobis(4-methoxy-2,4-dimethyl valeronitrile),2,2′-azobis(2,4-dimethyl valeronitrile), dimethyl2,2′-azobis(2-methylpropionate), and the like. Suitableperoxide-compound thermal initiators are exemplified by tert-amylperoxybenzoate, benzoyl peroxide, 2,2-bis(tert-butylperoxy)butane,1,1-bis(tert-butylperoxy)cyclohexane,2,5-bis(tert-butylperoxy)-2,5-dimethylhexane,2,5-bis(tert-butylperoxy)-2,5-dimethyl-3-hexyne,bis(1-(tert-butylperoxy)-1-methylethyl)benzene,1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, tert-butylhydroperoxide, tert-butyl peroxide, tert-butyl peracetate, cyclohexanoneperoxide, dicumyl peroxide, lauroyl peroxide, and the like.

Suitable solvents for preparing a resilient cation exchange membraneusing homogenous solution comprising a hydrophilic ionic monomer, ahydrophobic cross-linking oligomer and/or a comonomer, and a freeradical initiator, are exemplified by a mixture of dimethylacetamide andtributylamine at a ratio of about 1:3 to about 5:1, a mixture of,dimethylacetamide and trialkylamine at a ratio of about 1:3 to about5:1, a mixture of dimethylacetamide and dialkylamine at a ratio of about1:3 to about 5:1, and a mixture of dimethylacetamide and monoalkylamineat a ratio of about 1:3 to about 5:1. Particularly suitable is a mixtureof dimethylacetamide and tributylamine at a ratio of about 1:3 to about5:1. Also suitable is dimethylacetamide at a concentration of about 20%by weight of the homogenous solution to about 45% by weight of thehomogenous solution.

Suitable solvents for preparing a resilient anion exchange membraneusing homogenous solution comprising a hydrophilic ionic monomer, ahydrophobic cross-linking oligomer and/or a comonomer, and a freeradical initiator, are saturated aliphatic fatty acids exemplified bybutyric acid, valeric acid, caprylic acid, capric acid, hexanoic acid,lauric acid, palmitic acid, stearic acid, arachidic acid, behenic acid,and mixtures thereof. The concentration for the saturated aliphatic acidshould be in the range of about 23% by weight of the homogenous solutionto about 48% by weight of the homogenous solution. Also suitablesolvents for producing the resilient anion exchange membranes of thepresent invention are diethylene glycol, diethylene glycol methylesters, and mixtures thereof. Particularly suitable are mixtures ofdiethylene glycol and diethylene glycol methyl esters at a ratio ofabout 1:1.15 to about 2:1, wherein the concentration of the diethyleneglycol:diethylene glycol methyl ester mixture in the homogenous solutionis from a range of 32% by weight to about 42% by weight.

An exemplary process for producing a resilient cation ion exchangemembrane comprises:

1) preparing a homogenous solutions comprising: (i) about 15% to about35% of a suitable hydrophilic ionic monomer, (i) about 30% to about 65%of one or more suitable hydrophobic cross-linking oligomers and/orhydrophobic cross-linking comonomers, (iii) about 17% to about 45% ofone or more suitable solvents, and (iv) about 0.75% to about 10% of afree radical initiator;

2) saturating a porous matrix with the homogenous solution, thenremoving excess solution thereby producing a porous matrix impregnatedwith and covered by a film of the homogenous solution;

3) curing the impregnated porous matrix by activating the free radicalinitiator thereby causing formation of a homogenous polymeric gelwithin, throughout, and about the porous matrix thereby forming aresilient ion exchange membrane; and

4) washing the ion exchange membrane to remove excess solvent, thenbathing the membrane in a sodium chloride solution to convert themembrane into a sodium form thereby producing a resilient cationexchange membrane of the present invention.

Another exemplary process for producing a resilient cation ion exchangemembrane comprises:

1) preparing a homogenous solutions comprising: (i) about 20% to about30% of a suitable hydrophilic ionic monomer, (i) about 35% to about 60%of one or more suitable hydrophobic cross-linking oligomers and/orhydrophobic cross-linking comonomers, (iii) about 20% to about 35% ofone or more suitable solvents, and (iv) about 1.0% to about 2.5% of afree radical initiator;

2) saturating a porous matrix with the homogenous solution, thenremoving excess solution thereby producing a porous matrix impregnatedwith and covered by a film of the homogenous solution;

3) curing the impregnated porous matrix by activating the free radicalinitiator thereby causing formation of a homogenous polymeric gelwithin, throughout, and about the porous matrix thereby forming aresilient ion exchange membrane; and

4) washing the ion exchange membrane to remove excess solvent, thenbathing the membrane in a sodium chloride solution to convert themembrane into a sodium form thereby producing a resilient cationexchange membrane of the present invention.

An exemplary process for producing a resilient anion exchange membranecomprises:

1) preparing a homogenous solutions comprising: (i) about 15% to about35% of a suitable hydrophilic ionic monomer, (i) about 30% to about 45%of one or more suitable hydrophobic cross-linking oligomers and/orhydrophobic cross-linking comonomers, (iii) about 20% to about 45% ofone or more suitable solvents, and (iv) about 0.75% to about 10% of afree radical initiator;

2) saturating a porous matrix with the homogenous solution, thenremoving excess solution thereby producing a porous matrix impregnatedwith and covered by a film of the homogenous solution;

3) curing the impregnated porous matrix by activating the free radicalinitiator thereby causing formation of a homogenous polymeric gelwithin, throughout, and about the porous matrix thereby forming aresilient ion exchange membrane; and

4) washing the ion exchange membrane to remove excess solvent, thenbathing the membrane in a sodium chloride solution to convert themembrane into a chloride form thereby producing a resilient anionexchange membrane of the present invention.

Another exemplary process for producing a resilient anion exchangemembrane comprises:

1) preparing a homogenous solutions comprising: (i) about 20% to about30% of a suitable hydrophilic ionic monomer, (i) about 35% to about 40%of one or more suitable hydrophobic cross-linking oligomers and/orhydrophobic cross-linking comonomers, (iii) about 25% to about 40% ofone or more suitable solvents, and (iv) about 1.0% to about 2.5% of afree radical initiator;

2) saturating a porous matrix with the homogenous solution, thenremoving excess solution thereby producing a porous matrix impregnatedwith and covered by a film of the homogenous solution;

3) curing the impregnated porous matrix by activating the free radicalinitiator thereby causing formation of a homogenous polymeric gelwithin, throughout, and about the porous matrix thereby forming aresilient ion exchange membrane; and

4) washing the ion exchange membrane to remove excess solvent, thenbathing the membrane in a sodium chloride solution to convert themembrane into a chloride form thereby producing a resilient anionexchange membrane of the present invention.

The resilient cation exchange membranes of the present invention havethe following characteristics:

(i) membrane thickness in the range of about 0.06 mm to about 0.15 mm,of about 0.8 mm to about 0.13 mm, of about 0.9 mm to about 0.12 mm;

(ii) electrical resistance in the range of about 0.8 Ω cm² to about 3.0Ω cm², from about 1.0 to about 2.5 Ω cm², from about 1.1 Ω cm² to about2.1 Ω cm²;

(iii) water content in the range of about 20% to about 45% by wt., fromabout 25 to about 40% by wt., from about 29% to about 36% by wt.; and

(iv) ion exchange capacity from the range of about 1.3 mmol to about 2.5mmol per g of dry resin, 1.5 mmol to about 2.2 mmol per g of dry resin,1.8 mmol to about 2.0 mmol per g of dry resin.

The resilient anion exchange membranes of the present invention have thefollowing characteristics:

(i) membrane thickness in the range of about 0.06 mm to about 0.15 mm,of about 0.8 mm to about 0.13 mm, of about 0.9 mm to about 0.12 mm;

(ii) electrical resistance in the range of about 0.8 Ω cm² to about 3.0Ω cm², from about 1.0 to about 2.5 Ω cm², from about 1.1 Ω cm² to about2.1 Ω cm²;

(iii) water content in the range of about 20% to about 45% by wt., fromabout 25 to about 40% by wt., from about 29% to about 36% by wt.; and

(iv) ion exchange capacity from the range of about 1.3 mmol to about 2.5mmol per g of dry resin, 1.5 mmol to about 2.2 mmol per g of dry resin,1.8 mmol to about 2.0 mmol per g of dry resin.

The resilient ion exchange membranes of the present invention aredurable under fluctuating stress-strain pressure conditions, and areparticularly suitable for applications such as those exemplified bydesalinization of saline water, purification of drinking water,wastewater treatment, demineralization of amino acids, processing ofwhey waste streams, production of sugar liquors, de-salting dieselfuels, purification of organic substances, recovery of useful componentsfrom fluid process waste streams e.g., recovery metal ions fromelectroplating systems, among others.

The present invention will be further illustrated in the followingexamples. However it is to be understood that these examples are forillustrative purposes only, and should not be used to limit the scope ofthe present invention in any manner.

EXAMPLES Example 1 Preparation of an Exemplary Cation Exchange Membrane

A solvent solution was prepared by mixing together 152 g ofdimethylacetamide with 152 g of tributylamine. 304 g of the hydrophilicmonomer 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) was mixedinto the dimethylacetamide/tributylamine solvent solution and dissolved.228 g of hydrophobic cross-linking polyurethane oligomer diacrylate wasdiluted with 228 g of comonomer hexanediol diacrylate, and then wasadded to the solvent solution already containing the AMPS component. Themixture was stirred to form a homogenous solution after which, 15 g ofthe photoinitiator Irgacure® 2959 (Irgacure is a registered trademark ofCIBA Specialty Chemicals Corp., Tarrytown, N.Y., USA) was added anddissolved in the solvent mixture comprising the hydrophilic monomer andthe hydrophobic cross-linking oligomers and comonomers. The completehomogenous solution was applied onto a woven fabric comprising SEFAR®PET 1500 having the following physical properties: (i) mesh size 151 μm,(ii) open area 53%, and (iii) mesh thickness 90 μm (SEFAR is aregistered trademark of Sefar Holding AG, Thal, Switzerland). Excesshomogenous solution was removed from the woven polyester cloth byrunning a roller over the fabric with care taken to remove and excludeair bubbles from the within and about the woven fabric thereby producinga homogenous solution impregnated woven fabric. The impregnated wovenfabric was irradiated with UV light (wavelength 300-400 nm) for 8 min toinitiate polymerization of the hydrophilic monomer and the hydrophobicoligomer and comonomer, resulting in the formation of a homogenouspolymeric gel within, throughout, and about the woven fabric forming ahomogenous membrane structure. The resulting membrane was rinsedthoroughly in water and was then placed in 10% NaCl solution to enableion exchange to convert the membrane into a sodium form, therebyconverting the ion exchange membrane into a cation exchange membrane.The cation exchange membrane had the following properties:

Membrane thickness: 0.09 mm-0.10 mm

Electrical resistance: 2.1-2.5 Ω cm²

Water content: 29-31 wt %

Ion exchange capacity: 1.9 mmol per gram of dry resin

Example 2 Preparation of an Exemplary Cation Exchange Membrane Using aSingle Solvent System

304 g of AMPS was mixed with 304 g of tributylamine solvent (1:1). Itwas not possible to completely dissolve AMPS in the tributylaminesolvent i.e., this mixture did not form a homogenous solution.Subsequently, 200 g of AMPS was mixed with 304 g of tributylaminesolvent (1:1.5). It was not possible to completely dissolve AMPS in thetributylamine solvent i.e., this mixture did not form a homogenoussolution. Accordingly, it was determined that preparation of a cationexchange membrane having AMPS as the hydrophilic ion exchange componentrequired the addition of dimethylacetamide to the solvent solution.

Example 3 Preparation of an Exemplary Anion Exchange Membrane

To 360 g of hexanoic acid was added 201 g of the hydrophilic monomer3-methacryloylaminopropyl trimethylammonium chloride (MAPTAC) and wasgently stirred until the MAPTAC was dissolved. 394 g of the hydrophobiccross-linking oligomer polyurethane oligomer diacrylate was diluted with394 g of hydrophobic cross-linking comonomer hexanediol diacrylate, andthen stirred into the MAPTAC solution. After the mixture had dissolvedinto a homogenous solution, 15 g of Irgacure® 2959 was then stirred intoand dissolved in the homogenous solution. The homogenous solution wasapplied onto a woven fabric comprising SEFAR® PET 1500 having the sameproperties disclosed in Example 1. Excess solution was removed from thesubstrate by running a roller over the substrate with care being takento exclude air bubbles from the substrate. Excess homogenous solutionwas removed from the woven polyester cloth by running a roller over thefabric with care taken to remove and exclude air bubbles from the withinand about the woven fabric thereby producing a homogenous solutionimpregnated woven fabric. The impregnated woven fabric was irradiatedwith UV light (wavelength 300-400 nm) for 8 min to initiatepolymerization of the hydrophilic monomer and the hydrophobic oligomerand comonomer, resulting in the formation of a homogenous polymeric gelwithin, throughout, and about the woven fabric forming a homogenousmembrane structure. The resulting membrane was rinsed thoroughly inmethanol to remove hexanoic acid solvent, and then was placed in 10%NaCl solution to enable ion exchange to convert the membrane into achloride form, thereby converting the ion exchange membrane into ananion exchange membrane. The anion exchange membrane had the followingproperties:

Membrane thickness: 0.09-0.10 mm

Electrical resistance: 1.5-2.0 Ω cm²

Water content: 36-40 wt %

Ion exchange capacity: 1.6 mmol per gram of dry resin

Example 4 Electrodialysis Performance of Paired Cation ExchangeMembranes and Anion Exchange Membranes

A 24-cell electrodialysis microstack was assembled with cell pairscomprising alternating 3-inch by 3-inch sheets of the cation exchangemembranes produced in Example 1 and the anion exchange membranesprepared in Example 3. A salt solution comprising a mixture of CaCl₂ andNaCl (30 mS/cm, ˜18,000 mg/L TDS) was passed in parallel through thedilute/feed chambers and the brine/concentrate chambers of theelectrodialysis microstack at a rate of about 0.4 liter per hour. Adirect current of 50-90 mA was applied between the electrodes. Ionconcentrations in the dilute stream exiting the electrodialysismicrostack were measured after 19 hrs, 28 hrs and 44 hrs of operation.The data in FIG. 1 show that the concentrations of all three ions, i.e.,sodium, chloride and calcium, decreased steadily throughout the 44-hrmonitoring period.

Example 5 Diffusion Dialysis in a Diffusion Dialysis Stack Equipped withAnion Exchange Membranes

A 22-cell diffusion dialysis microstack was assembled with cell pairscomprising the anion exchange membranes prepared in Example 3. A saltsolution comprising a mixture of HCL (17 mg/mL) CaCl₂ (24.3 mg/mL) andNaCl (4.3 mg/mL) was passed through the feed chambers and whilede-ionized water was passed through the product chambers of thediffusion dialysis microstack at a rate of about 0.4 liter per hour. ThepH and the conductivity of the feed solution and the product solutionexiting the diffusion dialysis microstack were measured time 0, after 3hrs, and 40 hrs of operation. The data in Table 1 shows the pH and theconductivity of the feed solution and the product solution during the40-hr time period. Due to diffusion of the HCL from the feed side to theproduct side of the cell pairs, the pH of the outgoing feed flowincreased while its conductivity decreased, while the pH of the outgoingproduct flow decreased and its conductivity increased. Ion analysesshowed that there no calcium ions were present and only trace amounts ofsodium ions were present in the final solution of product flow.

TABLE 1 Feed Solution Product Solution conductivity conductivity Time pH(mS/cm) pH (mS/cm) 0 0.2 206 5.3 0.1  3 hr 0.4 189 1.5 14 40 hr 0.5 1170.5 110

Example 6 Regeneration of a Fouled Exemplary Ion Exchange Membrane

After extended use in electrodialysis systems, cation exchange membranesgenerally become fouled by the accumulation of divalent and/ormultivalent mineral ions about the membrane surfaces. Fouling of thecation exchange membrane produced in Example 1 was simulated bysubmersing and soaking the cation exchange membrane in a 5% CaCl₂solution for 24 hr. The electrical resistance of the membrane increasedfrom 2.2 Ω cm² prior to soaking to 8.5 Ω cm² after 24 hr of soaking inCaCl₂ indicating that the membrane was fouled by the calcium ions. Thefouled membrane was then submersed and soaked in a 3M NaCl solution for1 hr after which it was removed and its electrical resistance measuredagain. The electrical resistance was 2.2 Ω cm² indicating that thecation exchange membrane had been regenerated to its original condition.

Example 7 Preparation of an Exemplary Cation Exchange Membrane

To 304 g of the solvent dimethylacetamide (DMAc) was added 304 g of AMPSand was gently stirred until the AMPS was dissolved. Then, 380 g of thehydrophobic cross-linking comonomer hexanediol diacrylate was stirredinto the AMPS/DMAc solution. After the hexanediol diacrylate wasdissolved, 15 g of Irgacure® 2959 was then stirred into and dissolved inthe homogenous solution. The homogenous solution was applied onto a90-μm thick non-woven polypropylene substrate sheet with 80% porosity(DelStar Technologies Inc., Middleton, Del., USA). Excess homogenoussolution was removed from the non-woven porous substrate sheet byrunning a roller over the sheet with care taken to remove and excludeair bubbles thereby producing a non-woven substrate impregnated with andcovered by a film of the homogenous solution. The impregnated non-wovensubstrate was then irradiated with UV light (wavelength 300-400 nm) for8 min to initiate polymerization of the hydrophilic monomer and thehydrophobic cross-linking comonomer, resulting in the formation of ahomogenous polymeric gel within, throughout, and about the non-wovensubstrate forming a homogenous membrane structure. The resultingmembrane was rinsed thoroughly in water and was then placed in 10% NaClsolution to enable ion exchange to convert the membrane into a sodiumform, thereby converting the ion exchange membrane into a cationexchange membrane. The cation exchange membrane had the followingproperties:

Membrane thickness: 0.10 mm-0.12 mm

Electrical resistance: 1.1-1.5 Ω cm²

Water content: 29-31 wt %

Ion exchange capacity: 2.1 mmol per gram of dry resin

Example 8 Preparation of an Exemplary Cation Exchange Membrane

To 330 g of the solvent dimethylacetamide (DMAc) was added 252 g of AMPSand was gently stirred until the AMPS was dissolved. Then, 205 g ofhydrophobic cross-linking comonomer hexanediol diacrylate was dilutedwith 195 g of the cross-linking comonomer decanediol diacrylate and thenstirred into the AMP S/DMAc solution. After a homogenous solution wasformed, 18 g of Irgacure® 2959 was then stirred into and dissolved inthe homogenous solution. The homogenous solution was applied onto a100-μm thick microporous polyethylene membrane with 82% porosity (LydallFiltration/Separation Inc., Rochester, N.H., USA). Excess homogenoussolution was removed from the microporous membrane by running a rollerover the membrane with care taken to remove and exclude air bubblesthereby producing a microporous polyethylene membrane impregnated withand covered by a film of the homogenous solution. The impregnatedmicroporous polyethylene membrane was irradiated with UV light(wavelength 300-400 nm) for 8 min to initiate polymerization of thehydrophilic monomer and the hydrophobic comonomer, resulting in theformation of a homogenous polymeric gel within, throughout, and aboutthe microporous substrate forming a homogenous membrane structure. Theresulting membrane was rinsed thoroughly in water to remove excess DMAcand was then placed in 10% NaCl solution to enable ion exchange toconvert the membrane into a sodium form, thereby converting the ionexchange membrane into a cation exchange membrane. The cation exchangemembrane had the following properties:

Membrane thickness: 0.12 mm

Electrical resistance: 2.0 Ω cm²

Water content: 30-33 wt %

Ion exchange capacity: 2.3 mmol per gram of dry resin

Example 9 Preparation of an Exemplary Cation Exchange Membrane

To 231 g of the solvent dimethylacetamide (DMAc) was added 231 g of AMPSand was gently stirred until the AMPS was dissolved. Then, a mixture wasprepared by stirring together 327 g of hydrophobic comonomer hexanedioldiacrylate and 83 g of the hydrophobic comonomer laurel acrylate. Themixture of hydrophobic comonomers as added into the AMPS/DMAc solutionand stirred until a homogenous solution was formed. Then, 18 g ofIrgacure® 2959 was stirred into and dissolved in the homogenoussolution. The homogenous solution was applied onto a 90-μm thicknon-woven polypropylene substrate sheet with 80% porosity (DelStarTechnologies Inc.). Excess homogenous solution was removed from thenon-woven porous substrate sheet by running a roller over the sheet withcare taken to remove and exclude air bubbles thereby producing anon-woven substrate impregnated with and covered by a film of thehomogenous solution. The impregnated non-woven substrate was thenirradiated with UV light (wavelength 300-400 nm) for 8 min to initiatepolymerization of the hydrophilic monomer and the hydrophobiccomonomers, resulting in the formation of a homogenous polymeric gelwithin, throughout, and about the non-woven substrate forming ahomogenous membrane structure. The resulting membrane was rinsedthoroughly in water to remove excess DMAc and was then placed in 10%NaCl solution to enable ion exchange to convert the membrane into asodium form, thereby converting the ion exchange membrane into a cationexchange membrane. The cation exchange membrane had the followingproperties:

Membrane thickness: 0.09-0.12 mm

Electrical resistance: 1.5-2.0 Ω cm²

Water content: 30-33 wt %

Ion exchange capacity: 1.7 mmol per gram of dry resin

Example 10 Preparation of an Exemplary Anion Exchange Membrane

To a solvent solution comprising a mixture of 169 g of diethylene glycoland 213 g of diethylene glycol methyl ether was added 212 g of thehydrophilic monomer vinylbenzyl trimethylammonium chloride (VBTAC), andwas gently stirred until the VBTAC was completely dissolved. Then, 396 gof the hydrophobic cross-linking comonomer hexanediol diacrylate wasadded to the VBTAC solvent solution and stirred until the hexanedioldiacrylate was dissolved and a homogenous solution was formed. 10 g ofIrgacure® 2959 was then stirred into and dissolved in the homogenoussolution. The homogenous solution was applied onto a 90-μm thicknon-woven polypropylene substrate sheet with 80% porosity (DelStarTechnologies Inc.). Excess homogenous solution was removed from thenon-woven porous substrate sheet by running a roller over the sheet withcare taken to remove and exclude air bubbles thereby producing anon-woven substrate impregnated with and covered by a film of thehomogenous solution. The impregnated non-woven substrate was irradiatedwith UV light (wavelength 300-400 nm) for 10 min to initiatepolymerization of the hydrophilic monomer and the hydrophobic comonomer,resulting in the formation of a homogenous polymeric gel within,throughout, and about the non-woven substrate forming a homogenousmembrane structure. The resulting membrane was rinsed thoroughly inwater to remove excess diethylene glycol and diethylene glycol methylether, and then was placed in 10% NaCl solution to enable ion exchangeto convert the membrane into a chloride form, thereby converting the ionexchange membrane into an anion exchange membrane. The anion exchangemembrane had the following properties:

Membrane thickness: 0.09-0.12 mm

Electrical resistance: 1.1-1.5 Ω cm²

Water content: 36-40 wt %

Ion exchange capacity: 1.6 mmol per gram of dry resin

Example 11 Preparation of an Exemplary Anion Exchange Membrane

To a solvent solution comprising a mixture of 156 g of diethylene glycoland 227 g of diethylene glycol methyl ether was added 210 g of thehydrophilic monomer MAPTAC and was gently stirred until the MAPTAC wasdissolved. Then, 396 g of the hydrophobic cross-linking comonomerhexanediol diacrylate was mixed into the MAPTAC solution. After themixture had dissolved into a homogenous solution, 11 g of Irgacure® 2959was then stirred into and dissolved in the homogenous solution. Thehomogenous solution was applied onto a woven fabric comprising SEFAR®PET 1500 having the same properties disclosed in Example 1. Excesssolution was removed from the substrate by running a roller over thesubstrate with care being taken to exclude air bubbles from thesubstrate. Excess homogenous solution was removed from the wovenpolyester cloth by running a roller over the fabric with care taken toremove and exclude air bubbles from the within and about the wovenfabric thereby producing a homogenous solution impregnated woven fabric.The impregnated woven fabric was irradiated with UV light (wavelength300-400 nm) for 8 min to initiate polymerization of the hydrophilicmonomer and the hydrophobic comonomer, resulting in the formation of ahomogenous polymeric gel within, throughout, and about the woven fabricforming a homogenous membrane structure. The resulting membrane wasrinsed thoroughly in water to remove excess diethylene glycol anddiethylene glycol methyl ether, and then was placed into a 10% NaClsolution to enable ion exchange to convert the membrane into a chlorideform, thereby converting the ion exchange membrane into an anionexchange membrane. The anion exchange membrane had the followingproperties:

Membrane thickness: 0.07 mm

Electrical resistance: 1.5 Ω cm²

Water content: 34-38 wt %

Ion exchange capacity: 1.5 mmol per gram of dry resin

Example 12 Preparation of an Exemplary Cation Exchange Membrane

A solvent solution was prepared by mixing together 231 g ofdimethylacetamide with 77 g of tributylamine (3:1 ratio). To the 308-gsolvent mixture was added 304 g of AMPS and mixed until it wasdissolved. 114 g of hydrophobic cross-linking polyurethane oligomerdiacrylate was diluted with 342 g of comonomer hexanediol diacrylate(ratio of 1:3), and then was added to the solvent solution alreadycontaining the AMPS component. The mixture was stirred to form ahomogenous solution after which, 16 g of the photoinitiator Irgacure®2959 was added and dissolved in the solvent mixture comprising thehydrophilic monomer and the hydrophobic cross-linking oligomers. Thecomplete homogenous solution was applied onto a SEFAR® PET 1500 wovenfabric. Excess homogenous solution was removed from the woven polyestercloth by running a roller over the fabric with care taken to remove andexclude air bubbles from the within and about the woven fabric therebyproducing a homogenous solution impregnated woven fabric. Theimpregnated woven fabric was irradiated with UV light (wavelength300-400 nm) for 8 min to initiate polymerization of the hydrophilicmonomer and the hydrophobic oligomer and comonomer, resulting in theformation of a homogenous polymeric gel within, throughout, and aboutthe woven fabric forming a homogenous membrane structure. The resultingmembrane was rinsed thoroughly in water and was then placed in 10% NaClsolution to enable ion exchange to convert the membrane into a sodiumform, thereby converting the ion exchange membrane into a cationexchange membrane. The cation exchange membrane had the followingproperties:

Membrane thickness: 0.09 mm-0.10 mm

Electrical resistance: 2.0-3.0 Ω cm²

Water content: 25 wt %

Ion exchange capacity: 1.9 mmol per gram of dry resin

Example 13 Preparation of an Exemplary Cation Exchange Membrane

A solvent solution was prepared by mixing together 231 g ofdimethylacetamide with 77 g of tributylamine (3:1 ratio). To the 308-gsolvent mixture was added 304 g of AMPS and mixed until it wasdissolved. 177 g of hydrophobic cross-linking polyurethane oligomerdiacrylate was diluted with 531 g of comonomer hexanediol diacrylate(ratio of 1:3), and then was added to the solvent solution alreadycontaining the AMPS component. The mixture was stirred to form ahomogenous solution after which, 20 g of the photoinitiator Irgacure®2959 was added and dissolved in the solvent mixture comprising thehydrophilic monomer and the hydrophobic cross-linking oligomers. Thecomplete homogenous solution was applied onto a SEFAR® PET 1500 wovenfabric. Excess homogenous solution was removed from the woven polyestercloth by running a roller over the fabric with care taken to remove andexclude air bubbles from the within and about the woven fabric therebyproducing a homogenous solution impregnated woven fabric. Theimpregnated woven fabric was irradiated with UV light (wavelength300-400 nm) for 8 min to initiate polymerization of the hydrophilicmonomer and the hydrophobic oligomer and comonomer, resulting in theformation of a homogenous polymeric gel within, throughout, and aboutthe woven fabric forming a homogenous membrane structure. The resultingmembrane was rinsed thoroughly in water and was then placed in 10% NaClsolution to enable ion exchange to convert the membrane into a sodiumform, thereby converting the ion exchange membrane into a cationexchange membrane. The cation exchange membrane had the followingproperties:

Membrane thickness: 0.09 mm-0.10 mm

Electrical resistance: 3.5-4.0 Ω cm²

Water content: 22 wt %

Ion exchange capacity: 1.4 mmol per gram of dry resin

Example 14 Preparation of an Exemplary Cation Exchange Membrane

A solvent solution was prepared by mixing together 231 g ofdimethylacetamide with 77 g of tributylamine (3:1 ratio). To the 308-gsolvent mixture was added 304 g of AMPS and mixed until it wasdissolved. 76 g of hydrophobic cross-linking polyurethane oligomerdiacrylate was diluted with 228 g of comonomer hexanediol diacrylate(ratio of 1:3), and then was added to the solvent solution alreadycontaining the AMPS component. The mixture was stirred to form ahomogenous solution after which, 14 g of the photoinitiator Irgacure®2959 was added and dissolved in the solvent mixture comprising thehydrophilic monomer and the hydrophobic cross-linking oligomers. Thecomplete homogenous solution was applied onto a SEFAR® PET 1500 wovenfabric. Excess homogenous solution was removed from the woven polyestercloth by running a roller over the fabric with care taken to remove andexclude air bubbles from the within and about the woven fabric therebyproducing a homogenous solution impregnated woven fabric. Theimpregnated woven fabric was irradiated with UV light (wavelength300-400 nm) for 8 min to initiate polymerization of the hydrophilicmonomer and the hydrophobic oligomer and comonomer, resulting in theformation of a homogenous polymeric gel within, throughout, and aboutthe woven fabric forming a homogenous membrane structure. The resultingmembrane was rinsed thoroughly in water and was then placed in 10% NaClsolution to enable ion exchange to convert the membrane into a sodiumform, thereby converting the ion exchange membrane into a cationexchange membrane. The cation exchange membrane had the followingproperties:

Membrane thickness: 0.09 mm-0.10 mm

Electrical resistance: 1.2-1.5 Ω cm²

Water content: 35 wt %

Ion exchange capacity: 2.4 mmol per gram of dry resin

Example 15 Preparation of an Exemplary Cation Exchange Membrane

A solvent solution was prepared by mixing together 203 g ofdimethylacetamide with 88 g of tributylamine (2.3:1 ratio). To the 291-gsolvent mixture was added 304 g of AMPS and mixed until it wasdissolved. 340 g of hydrophobic cross-linking polyester oligomerdiacrylate was diluted with 113 g of comonomer hexanediol diacrylate(ratio of 3:1), and then was added to the solvent solution alreadycontaining the AMPS component. The mixture was stirred to form ahomogenous solution after which, 15 g of the photoinitiator Irgacure®2959 was added and dissolved in the solvent mixture comprising thehydrophilic monomer and the hydrophobic cross-linking oligomers. Thecomplete homogenous solution was applied onto a SEFAR® PET 1500 wovenfabric. Excess homogenous solution was removed from the woven polyestercloth by running a roller over the fabric with care taken to remove andexclude air bubbles from the within and about the woven fabric therebyproducing a homogenous solution impregnated woven fabric. Theimpregnated woven fabric was irradiated with UV light (wavelength300-400 nm) for 8 min to initiate polymerization of the hydrophilicmonomer and the hydrophobic oligomer and comonomer, resulting in theformation of a homogenous polymeric gel within, throughout, and aboutthe woven fabric forming a homogenous membrane structure. The resultingmembrane was rinsed thoroughly in water and was then placed in 10% NaClsolution to enable ion exchange to convert the membrane into a sodiumform, thereby converting the ion exchange membrane into a cationexchange membrane. The cation exchange membrane had the followingproperties:

Membrane thickness: 0.09 mm-0.10 mm

Electrical resistance: 2.0-3.0 Ωcm²

Water content: 28 wt %

Ion exchange capacity: 1.9 mmol per gram of dry resin

Example 16 Preparation of an Exemplary Anion Exchange Membrane

To 360 g of hexanoic acid was added 210 g of the hydrophilic monomer3-methacryloylaminopropyl trimethylammonium chloride (MAPTAC) and wasgently stirred until the MAPTAC was dissolved. 70 g of the hydrophobiccross-linking polyurethane oligomer diacrylate was diluted with 140 g ofhydrophobic cross-linking comonomer hexanediol diacrylate (ratio of2:1), and then stirred into the MAPTAC solution. After the mixture haddissolved into a homogenous solution, 11 g of Irgacure® 2959 was thenstirred into and dissolved in the homogenous solution. The homogenoussolution was applied onto a SEFAR® PET 1500 woven fabric. Excesssolution was removed from the substrate by running a roller over thesubstrate with care being taken to exclude air bubbles from thesubstrate. Excess homogenous solution was removed from the wovenpolyester cloth by running a roller over the fabric with care taken toremove and exclude air bubbles from the within and about the wovenfabric thereby producing a homogenous solution impregnated woven fabric.The impregnated woven fabric was irradiated with UV light (wavelength300-400 nm) for 8 min to initiate polymerization of the hydrophilicmonomer and the hydrophobic oligomer and comonomer, resulting in theformation of a homogenous polymeric gel within, throughout, and aboutthe woven fabric forming a homogenous membrane structure. The resultingmembrane was rinsed thoroughly in methanol to remove hexanoic acidsolvent, and then was placed in 10% NaCl solution to enable ion exchangeto convert the membrane into a chloride form, thereby converting the ionexchange membrane into an anion exchange membrane. The anion exchangemembrane had the following properties:

Membrane thickness: 0.09-0.10 mm

Electrical resistance: 0.8-1.0 cm²

Water content: 36-46 wt %

Ion exchange capacity: 2.3 mmol per gram of dry resin

Example 17 Preparation of an Exemplary Anion Exchange Membrane

To 360 g of hexanoic acid was added 210 g of the hydrophilic monomer3-methacryloylaminopropyl trimethylammonium chloride (MAPTAC) and wasgently stirred until the MAPTAC was dissolved. 245 g of the hydrophobiccross-linking polyurethane oligomer diacrylate was diluted with 245 g ofhydrophobic cross-linking comonomer hexanediol diacrylate (at a ratio of1:1), and then stirred into the MAPTAC solution. After the mixture haddissolved into a homogenous solution, 15 g of Irgacure® 2959 was thenstirred into and dissolved in the homogenous solution. The homogenoussolution was applied onto a SEFAR® PET 1500 woven fabric. Excesssolution was removed from the substrate by running a roller over thesubstrate with care being taken to exclude air bubbles from thesubstrate. Excess homogenous solution was removed from the wovenpolyester cloth by running a roller over the fabric with care taken toremove and exclude air bubbles from the within and about the wovenfabric thereby producing a homogenous solution impregnated woven fabric.The impregnated woven fabric was irradiated with UV light (wavelength300-400 nm) for 8 min to initiate polymerization of the hydrophilicmonomer and the hydrophobic oligomer and comonomer, resulting in theformation of a homogenous polymeric gel within, throughout, and aboutthe woven fabric forming a homogenous membrane structure. The resultingmembrane was rinsed thoroughly in methanol to remove hexanoic acidsolvent, and then was placed in 10% NaCl solution to enable ion exchangeto convert the membrane into a chloride form, thereby converting the ionexchange membrane into an anion exchange membrane. The anion exchangemembrane had the following properties:

Membrane thickness: 0.09-0.10 mm

Electrical resistance: 3.5-4.0 Ω cm²

Water content: 36-34 wt %

Ion exchange capacity: 1.4 mmol per gram of dry resin

While particular embodiments have been described in this description, itis to be understood that other embodiments are possible and that theinvention is not limited to the described embodiments and instead aredefined by the claims.

What is claimed is:
 1. A resilient cation exchange membrane comprising aporous matrix selected from a group consisting of polyesters, polyvinylchlorides, low-density polyethylenes, very-low-density polyethylenes,polypropylenes, polysulfones, nylons, nylon-polyamides, and mixturesthereof, said porous matrix impregnated with a cross-linked homogenousion-transferring polymer that fills the pores and substantially coversthe surfaces of the porous matrix, said polymer formed by polymerizing ahomogeneous solution comprising (i) a hydrophilic ionic monomer selectedfrom a group consisting of 2-acrylamido-2-methyl-1-propanesulfonic acid,2-acrylamido-2-methyl-1-propanesulfonic acid salts, sodium4-vinylbenzenesulfonate, and 3-sulfopropyl acrylate potassium, with (ii)a hydrophobic cross-linking oligomer selected from a group consisting ofpolyurethane oligomer diacrylate, polyester oligomer diacrylate, epoxyoligomer diacrylate, polybutadiene oligomer diacrylate, siliconediacrylate, dimethacrylate counterparts thereof, polyurethane oligomershaving three or more vinyl groups, polyester oligomers having three ormore vinyl groups, and mixtures thereof.